MEH 4 - Energy Production (Carbohydrates)

Question 1

What is pyruvate dehydrogenase used for?

Answer 1

Converts pyruvate and Coenzyme A into acetyl CoA. This uses NAD+ and produces NADH and H+. Reaction is irreversible and is sensitive to vitamin B1 deficiency as it requires B-vitamins

Question 2

True or false - PDH is a simple structured enzyme?

Answer 2

False - it is a large multi-enzyme complex of five different enzymes

Question 3

Which co-factors does PDH require?

Answer 3

FAD, thiamine pyrophosphate and lipoid acid

Question 4

What substances activate PDH?

Answer 4

• Pyruvate
• CoASH
• NAD+
• ADP
• Insulin

Question 5

What substances inhibit PDH?

Answer 5

• acetyl-CoA
• NADH
• ATP
• citrate

Question 6

How many Krebs cycles occur per glucose molecule?

Answer 6

2

Question 7

Outline the Krebs cycle (no names required, just carbon numbers)

Answer 7

• acetyl CoA (C2) + C4 = C6 (citrate)
• citrate converted to another C6 molecule, then isocitrate (also C6)
• NADH and CO2 given off
• isocitrate converted to C5, more NADH and CO2 given off, C5 converted to C4 (succinylcoA)
• CoA and GTP given off, C4 converted to succinate (C4)
• succinate converted to fumarate (C4) giving off FADH2
• fumarate converted to malate (C4), taking in H2O
• malate converted to oxaloacetate (C4), giving off NADH

Question 8

How is the TCA (Krebs) cycle regulated?

Answer 8

• energy availability regulates it, so if not enough ATP or NADH is available then can’t function
• isocitrate dehydrogenase
• alpha-ketoglutarate dehydrogenase

Question 9

Is the Krebs cycle oxidative or reductive?

Answer 9

It is oxidative, producing NADH and FADH2

Question 10

What are the folds in mitochondria called?

Answer 10

Cristae

Question 11

How does the electron transport chain work?

Answer 11

NADH gives off 2H+, which are pumped into the intermembrane space by the proton translocating complex (PTC). FADH2 also does this. The electrons move from PTC to PTC, releasing energy, until they are eventually accepted by 2H+ and and oxygen to form H2O.

Question 12

What is the H+ gradient produced by the electron transport known as?

Answer 12

Proton motive force

Question 13

How does the proton motive force generate ATP?

Answer 13

• return of protons is favoured energetically by the electrochemical potential
• protons can only return across the membrane via the ATP synthase enzyme, which drives ATP synthesis

Question 14

How is oxidative phosphorylation regulated?

Answer 14

High [ATP] means there is low [ADP], so there is no substrate for ATP synthase. The outward flow of H+ stops, and [H+] in intermembrane space increases, preventing further pumping of H+ and electron transport. Reverses when ATP conc. lowers.

Question 15

How can oxidative phosphorylation be blocked?

Answer 15

Inhibitors block electron transport eg. Cyanide prevents acceptance of electrons by O2

Question 16

What do ‘uncouplers’ do in oxidative phosphorylation?

Answer 16

They increase the permeability of the mitochondrial inner membrane to protons. This dissipates the proton gradient, reducing the proton motive force. There is therefore no drive for ATP synthesis. Eg. Dinitrophenol

Question 17

How can oxidative phosphorylation diseases affect the ATP synthesis process?

Answer 17

Genetic defects in proteins encoded by mitochondrial DNA leads to decrease in electron transport

Question 18

What happens to the energy not used in oxidative phosphorylation?

Answer 18

It is lost as heat

Question 19

What is thermogenin (UCP1)?

Answer 19

A naturally occurring uncoupling protein

Question 20

How does brown adipose tissue generate heat?

Answer 20

• in response to cold, noradrenaline activates lipase which releases fatty acids
• oxidation of fatty acids produces NADH and FADH2 for electron transport
• fatty acids activate UCP1, which transports H+ back to mitochondria
• this means electron transport can occur uncoupled from ATP synthesis, so heat is generated

Question 21

Where is brown adipose tissue found?

Answer 21

• newborn infants to maintain heat around vital organs

- hibernating animals to generate heat to maintain body temp

Question 22

Outline the difference between oxidative and substrate level phosphorylation

Answer 22

OX PHOS-

• requires membrane-associated complexes
• energy coupling occurs directly through proton gradient
• requires O2
• major process in cells requiring lots of energy

SUBSTRATE LEVEL-

• requires soluble enzymes
• energy coupling occurs directly throuhg formation of high energy of hydrolysis bond
• can occur without O2 (limited)
• minor process in cells requiring large amounts of energy